DETAILED DESCRIPTION The polysilazane used in the practice of the invention may be any polysilazane that is soluble in common organic solvents, such as aliphatic or aromatic hydrocarbons or dialkyl or alicyclic ethers; and it may be, e.
g.
, a polysilazane of Seyferth et al.
-I, -II, -III, -IV, or -V or Arai et al.
, the teachings of all of which are incorporated herein by reference.
However, it is preferably a polysilazane of the type taught by Seyferth et al.
-II, i.
e.
, a polysilazane prepared by reacting an organodihalosilane, such as methyldichlorosilane, with ammonia and polymerizing the ammonolysis product with a basic deprotonation catalyst, such as potassium hydride.
Although the ceramic powder may be any of those taught above, it is preferably silicon carbide or a silicon carbide-containing mixture of powders.
A particularly preferred form of silicon carbide, especially when it is used primarily to provide heat or abrasion resistance, is alpha-silicon carbide.
As already mentioned, the ceramic powder may include up to 90% by weight of a metal boride, such as the borides or silicon, hafnium, titanium, niobium, zirconium, and the rare earth metals, or a mixture of a metal boride and zirconium metal.
When included, this optional component usually constitutes about 20-90%, preferably 20-50% by weight of the total ceramic powder; and it is preferably a silicon boride, i.
e.
, silicon tetraboride and/or silicon hexaboride.
It is preferred that the ceramic powder have an average particle size of about 0.
1-40 micrometers, most preferably about 0.
1-10 micrometers, to facilitate the formation of a homogeneous dispersion.
However, finer or coarser particles are also utilizable.
The amount of ceramic powder used may be anywhere in the range of about 0.
4-3.
0 parts, preferably about 0.
5-1.
5 parts per part by weight of the polysilazane, although the smaller amounts are apt to be preferred when the powder is employed to provide heat or abrasion resistance, while the larger amounts are preferred when the objective of incorporating the powder is primarily to provide oxidation resistance
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